FR2775913A1 - Flame spraying aluminum coatings on highly corrosive metallic vehicle body components - Google Patents

Abstract

A protective layer is applied to the surface of a component for treatment by blasting to activate the component surface. The component is then sprayed. Both blasting and spraying steps are performed in the same apparatus.

Description

The invention relates to a method of depositing a protective layer on

  surfaces of a part to be treated comprising: - a spraying operation to activate the part by means of a material to be sprayed and at least one spraying operation

  verification to coat the part using an installation

  spraying system, a spraying installation and a supply installation of material to be sprayed and sprayed,

  to improve their resistance capacity.

  In such spraying methods as for example spraying according to the HVOF (High Velocity Oxygen Fuel) rapid oxygen spraying process, generally the surface to be treated of a part or of a component is, in a

  first step, subject to the projection of a pro-

  jection which is for example aluminum oxide (A1203) or silicon carbide (SiC). This step is carried out with a projection device intended only for this purpose and which is generally a spray gun. By a corresponding air supply of this spray gun, an injection effect is obtained in a reservoir containing the material

  to project; this effect sucks the material to be sprayed from the

  storage tank and accelerates it into the gun. The trai-

  The surface with the material to be sprayed causes an "activation" of the surface subjected to the spraying. This surface is thus granulated, which increases its surface and

  thus allows better adhesion of the layers deposited ul-

  later. In addition, treatment with a material to pro-

  discarding cleans the surface to be treated, eliminating residues such as oxidized skins from the manufacture of the part to be treated. In known methods, after spraying onto the surface, a second step of the spraying operation is carried out in which the surface to be treated is covered with another spraying device.

  specially planned for this stage.

  The disadvantage of this process is that it uses a planned installation for each of the two process steps.

  only for this purpose. It is thus necessary to plan an installation

  projection in which the part to be treated owes everything

  first be activated as described above. This requires

  often site specially designed rooms or cabins

  for manual activation of the part to be treated. For the se-

  This stage of the operation requires thermal cabins in which the part must be transported, to then carry out the spraying operation with the installation of

  spraying provided for this purpose.

  In addition to the implementation of relatively large means for the two devices used in the two stages of the operation and the high purchase and maintenance costs, this method also has the drawback of

  not be suitable for the installation of an anti-

  corrosion on highly corrosive surfaces. In the future, the use of easily oxidizable materials such as for example magnesium or aluminum alloys, magnesium, titanium or copper-based materials, will become more important. These

  materials are particularly interesting for the cons-

  truction of vehicle bodies. In the process according to the state of the art, there is a time interval between

  the surface activation step and the spraying step

  tion during which an oxidation skin is formed on the

  surface of easily oxidizable materials which significantly lowers

  the attachment of the cover layer

later.

  Another disadvantage of the method used so far is that the sprayed material used to activate the surface of the part is recovered several times after it

  has been projected onto the surface to reduce the total amount

  tale of projected material. It is then returned to the tank after a cleaning step carried out in parallel to be used again for a spraying process. It

  results in a reduction in the abrasiveness of the projected particles

  tees so that during a long operation,

  efficiency decreases rapidly. In the field of trafficking-

  surface coating of highly corrosive light metals, it

  In this operation, there appears in particular the problem that, despite the cleaning of the projected materials already used,

  small impurities remain on them. These impurities pro-

  inter alia come from contact with the coating of the

  bine or friction against the walls of the tank or pipes or conduits. These parts of the installation are generally made of steel. This is why it remains, despite the net-

  cleaning, a certain amount of steel residue in the ma-

  sprayed material which is injected into the surface of the light metal part. Even when these impurities are covered by the layer deposited by the subsequent spraying, they

  constitute germs of corrosion on the surface of the part.

  The object of the invention is to propose a method of the above type increasing the resistance capacity of the

surface to be treated.

  To this end, the invention relates to a process

  characterized in that the spraying and spraying operations

  risation are carried out by the same installation.

  According to other interesting characteristics: * the shape and the consistency of the projected particles are not appreciably modified during the operation, * the temperature of the particles projected during the operation is below their melting point, * the operation of spraying and spraying takes place at the same time in a single process step,

  * we use as material to treat the surface an al-

  bonding of light metal, copper, nickel or a steel alloy, * the alloy of light metals is an alloy of aluminum or magnesium, * the proportion of the projected particles represents at least 10% and at most 50% by volume, * the size of the projected particles is between 5 and mm, * the coating material is aluminum, * the outlet temperature of the spraying and spraying installation is at least 2000 ° C. for the material to be sprayed or sprayed, * a layer of aluminum is deposited in places sensitive to

  corrosion of body frame elements.

  The method according to the invention can be used in general to deposit a protective layer and more particularly protection against corrosion or abrasion. The method according to the invention has the advantage of using a single installation for the treatment as well as for the coating of the part. This simplifies the entire installation for carrying out

  the operation, which reduces the cost of installation. In or-

  tre, we significantly reduce the time expenditure required

  res to the conduct of the operation and thus the costs of

manufacture of the part.

  A method in which the projection operation

  and spraying are carried out in the same pre-

  feels the advantage over the state of the art of ne-

  stop much less material to be sprayed. In the process

  according to the state of the art, the projected materials are

  dragged by pressurized air communicating to particles

  the projected speeds between 30 and 60 m / s. Due to the resulting particle energy, the treatment of the workpiece surface requires a large amount of

  particles. On the other hand, the acceleration of particles, pro-

  thrown into the process according to the invention, is done by a

  burning operation in the projection and re-

  covering. This operation delivers energy 10 times higher than the projected particles compared to those

  obtained according to the state of the art. Thus, only about forty

  proportionally low tity of particles (of the order of

  g / mn) is necessary to activate in the proportion exi-

  aged. Due to the low quantity of projected materials used

  read in the process according to the invention, it is not

  necessary to reuse these during the pro-

  jection, which eliminates the problem of corrosion of the part by the cleaned projection material. In connection with this, it is also particularly advantageous that the amount of particles used in the process according to

  the invention can be dosed much more pre-

  only in devices according to the state of the art.

  Because of the use of the same installation and the same apparatus for the spraying operation as well as for the spraying operation, it is advantageous that the

  surfaces treated by spraying and spraying respectively

  risation fit better. Contrary to this, in the process according to the state of the art, very often a larger surface is treated by projection than that which will be sprayed subsequently, so that the edge area

  is not covered. In the processing of metal parts

  highly corrosive, the edge area treated by

  jection, but not covered, attracts very corrosion

  important so that state-of-the-art processes

  are not suitable for packaging metal parts-

  highly corrosive liquids. On the contrary, the process according to

  the invention, using the same installation and the same apparatus

  reil for spraying and spraying operations, allows a more precise definition of the treated surfaces and thus ensures that there is no edge area which is not sprayed and subsequently oxidized. Due to this better definition of the treated surfaces, the method according to the invention increases significantly

protection against corrosion.

  The method according to the invention will be described below.

  after: The method according to the invention uses a single device or a single installation as

  that projection and spraying installation for reali-

  ser the spraying operation, and that of spraying. It is therefore no longer necessary to transfer the part to be treated from a projection chamber provided for this purpose according to the prior art, to a separate spray chamber for treating the part. Instead, the room can stay in

  one and the same chamber for the two stages of the process.

  Between the two process steps, simply switch the

  connection of the spraying and spraying installation

  between the reservoir of the material to be sprayed and the reservoir

  see material to be sprayed. This is done quickly and even highly corrosive metals do not have

time to start oxidizing.

  For the projection operation, we use

  preferably a powder as a spray material; advantageous

  This powder has a particle size such that the powder particles can no longer be welded together by the spray and spray gun. This prevents molten projection material from settling on the inside wall of the projection device. By the use of

  particles of minimum size for the pro-

  jection which preferably have a high melting point compared to the state of the art, these particles not being reused, they retain their initial shape at the outlet of the projection apparatus, that is to say their abrasion capacity. For these reasons, with the spraying operation according to the invention, optimal activation of the surface of the part to be treated is obtained and the operation of

  subsequent spraying, minimizing the risk

corrosion of the part.

  It is essential that the projected particles do not

  are not, even partially, welded together by fu-

  because it would change their consistency. Depending on the use, the particles should not have a sharp edge shape but may for example be produced in the form of beads. The activation of the treated surface is done

  then thanks to a relatively high hardness of the particles.

  In an alternative process, the materials projected

  tees and spray can also be brought in at the same time

  on the surface of the part to be treated. In this case, the material

  sprayed material and sprayed material are taken simultaneously

  in the corresponding tanks, so that the two re-

  towels are connected at the same time to the installation of

projection and spraying.

  For example, oxide particles are used

  aluminum (A1203) or silicon carbide (SiC) as ma-

  materials to be projected. In many applications of the process according to the invention, aluminum is used as a coating material. The portion of sprayed or abrasive material measured in the method according to the invention relative to the totality of the spraying and spraying material represents at least

  minimum 5% and maximum 50% of the mass and in the majority

  of the uses, the intended portion is 10% to 30% of

the mass.

  The particle size is between 5 gm

and 150 μm according to the invention.

  The method according to the invention offers particular advantages for the deposition of a layer of protection against corrosion on elements of vehicle body frames, which will be described later. In the case of vehicles subject to atmospheric conditions, humidity and

  water mixed with salt, enter inside the body-

  series and thus also at places where different metals touch, thus promoting corrosion. In future vehicles, bodies are provided, the outer casing of which will be made of sheet metal, such as sheet metal

  aluminum and the frame of the bodywork will be made of

  highly corrosive material such as magnesium or

  magnesium alloys. In the lower area of the coach-

  series, and also inside the bodywork where this water is found and often remains for a long time (cavity),

  in general, we refer to the corresponding location

  front of the magnesium element, sheets so that the bottom is not directly in contact with the highly corrosive frame elements. Corrosion could not

  so far be countered only very inadequately

  health, because the sheets of these places were not completely waterproof against standing water located in the bottom. Thanks to

  process according to the invention, it is now possible to

  put a layer of aluminum directly on the locations

  so that stagnant water is not in con-

  tact with magnesium, even in the long term.

  In conclusion, it should be noted that the invention relates to a method of depositing a protective layer on surfaces of a part to be treated and, in other words, a

  process for the preparation and thermal covering of surface

  these corrosives. Finally, this process applies in particular to the deposition of a layer of aluminum in places sensitive to corrosion.

  Zion of body frame elements.

Claims (8)

R E V E N D I C A T I ON S   1) Method of depositing a protective layer on surfaces   these of a part to be treated comprising - a spraying operation to activate the part by means of a material to be sprayed and at least one spraying operation   verification to coat the part using an installation   projection, a spraying installation and a supplying installation of spraying and spraying material, characterized in that   the spraying and spraying operations are carried out killed by the same facility.   2) Process for the preparation and thermal recovery of corrosive surfaces, according to claim 1, characterized in that the shape and the consistency of the projected particles are not   not significantly changed during the operation.   3) Process for the preparation and thermal recovery of corrosive surfaces, according to claim 1 or 2, characterized in that the temperature of the particles projected during the operation   is below their melting point.   4) Method of preparation and thermal recovery of   corrosive surfaces according to one of the preceding claims   tes, characterized in that the spraying and spraying operation is carried out   same time in one and the same process step.    ) Method of preparation and thermal recovery of   corrosive surfaces according to one of the preceding claims   tes, characterized in that an alloy is used as the material for treating the surface   light metal, copper, nickel or a steel alloy.   6) Method according to claim 5, characterized in that the light metal alloy is an aluminum or magnesium alloy.   7) Method according to one or more of the preceding claims   teeth, characterized in that the proportion of the projected particles represents at least 10% and not more than 50% by volume.   8) Method according to one or more of the preceding claims   teeth, characterized in that the size of the projected particles is between 5 and µm.   ) Method according to one of the preceding claims, characterized in that   the coating material is aluminum.    ) Method according to one of the preceding claims,   characterized in that the output temperature of the spraying and spraying installation is at least 2000 C for the material to be spray or spray.   11) Application of the method according to any one of the resales   previous instructions for depositing a layer of aluminum at places susceptible to corrosion of body frame elements.